BMWUSA.COM show 155mph as on option just like all 550i sold outside North-America.
http://www.bmwusa.com/Standard/Conte...fications.aspx
You can get the 155mph limiter on none M-Sport cars as well. On the 546 to this day built 550i/6 have 427 of them the 155MPH limiter and only 213 cars have M-Sport Package.
Regards Stephan